Piston crown cooling feature for diesel engines

ABSTRACT

Internal combustion diesel engines require localized cooling methods for the pistons in these engines. The lubricating oil for the engine is also used as a cooling medium. The operating temperature and stresses in the newest models of diesel engines are extremely high and approach the mechanical limits of the engine component materials. Therefore, supplemental methods are required to remove the excessive heat generated during engine operation. In order to increase the amount of heat transferred to the oil from the piston in a given time, a plurality of fins or grooves are formed on some of the heat transferring surfaces of the piston, such as inside the combustion bowl. The increased surface area of the component allows more heat to be dissipated to the oil that is in contact with the surface. The more heat removed from the piston, the more efficiently and economically the engine will perform in service.

BACKGROUND OF THE INVENTION

This invention embodies a method that providing increased cooling to the piston crown during operation in a diesel internal combustion engine. The new feature, integrated into the combustion bowl of the piston crown, improves engine power and reliability by increasing the amount of heat dissipation from the piston crown to the cooling oil as the oil circulates through the crown.

A diesel engine piston usually has a cooling cavity formed circumferentially around and outwardly of the outer periphery of the piston crown. A cooling liquid, usually oil, is directed into an inlet passageway. The oil circulates through the passage and removes heat from the piston.

The inside diameter of the cooling cavity is smaller adjacent to the top of the piston than the cavity adjacent to the bottom of the piston. The cross-sectional area of the cooling cavity gradually increases from the bottom of the cooling cavity toward the top of the cooling cavity.

Conventional diesel engine pistons sometimes have a concave surface that creates a combustion bowl. Some combustion bowls are inlaid with inverted cone shaped feature within the concave cavity. The tip of the cone is positioned perpendicular to the longitudinal axis of the piston and laterally in the center of the concave combustion bowl of the piston.

During normal engine operation, the piston is required to exhibit a significant resistance to heat load. A common and effective method used for the removal of the heat produced in the combustion bowl of the piston is the incorporation of a feature in the piston crown called a cooling gallery.

During operation, a cooling liquid is supplied to the cooling cavity through a cooling liquid inlet so as to cool the piston top face, including especially the interior of the annual section within the piston crown which becomes very hot during normal engine operation. The cross-sectional area of the cooling cavity in a plane containing the longitudinal axis of the piston is larger near the bottom of the cooling cavity than toward the top of the cooling cavity.

United States Patent Application Publication No. US 2014/0102294 to Klein discloses a two-piece piston with a cooling gallery having fins extending out from the bottom and/or the top of the cooling gallery. These fins act to increase the surface area of the piston that is cooled by the cooling oil. The fins are formed by machining the shape from the forged or cast cooling gallery block, using special tooling equipment. However, the shape of the fins can divide the gallery into chambers and adversely affect the flow of cooling oil through the gallery.

U.S. Pat. No. 6,532,913 to Opris also discloses a two-piece piston having a fin extending into the cooling gallery. This fin is either attached to or machined into the cooling gallery.

U.S. Pat. No. 4,368,697 to Moebus discloses a two-piece piston in which the cooling gallery is coated by a highly thermally conducting material. Ribs can be formed on the inside of the cooling gallery by the coating or by the underlying base material.

While these patents disclose features incorporated inside the cooling gallery, it would be desirable to incorporate cooling features in other parts of the piston as well.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a way to improve the effectiveness of the cooling oil, which can be used for all types of pistons and which does not require extra equipment and expense.

These and other objects are accomplished by a piston for an internal combustion engine, having a combustion bowl, a circumferential ring belt and a circumferential cooling gallery disposed between the combustion bowl and the ring belt. Pin bosses are disposed below the piston head, each pin boss having a pin bore. The combustion bowl has an interior surface with at least one fin disposed thereon. The fin increases the surface area of the combustion bowl, which shares a wall with the cooling gallery. The increased surface area leads to increased cooling of the piston. Preferably, there are several fins, which extend circumferentially around an upper region of the combustion bowl. In addition to the fins in the interior of the combustion bowl, there can be fins disposed on the interior walls of the cooling gallery as well. Furthermore, there can also be fins disposed underneath the combustion bowl.

In one embodiment, the cooling gallery is open at the bottom. A cover can be placed over the open bottom for sealing the bottom. The cover can also have an aperture for oil drainage. The fins can be formed from any desired method. In one embodiment, the fins are forged onto the surface of the combustion bowl. In another embodiment, the fins are machined into the surface of the combustion bowl. In a further embodiment, the fins are mounted or affixed to the surface via a mechanical method, such as with screws.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of specific embodiments can be best understood when read in conjunction with the following drawings.

FIG. 1 is a cross-sectional view of a piston according to the present invention;

FIG. 2 is an enlarged view of area II of FIG. 1;

FIG. 3 is an enlarged view similar to FIG. 2 showing a cooling oil aperture; and

FIG. 4 is a cross-sectional view of an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Operating conditions inside a diesel engine are severe. As the output of the engine increases, the piston is subjected to a high heat load and mechanical stress. The extremely hot operating temperatures may cause sections of the piston to deform, crack, or possibly melt. These failure modes result in a reduced engine performance and premature engine failure during even under normal operating conditions. By placing cooling fins at strategic locations in the piston, such as on the interior surface of the combustion bowl, the piston is better able to diffuse the heat created by the high loads and stresses, and is thus less vulnerable to damage.

As shown in FIG. 1, the piston 10 according to the invention has a piston head 11 with a combustion bowl 12, a top land 13 and a ring belt 14. A circumferential cooling gallery 15 is formed between the ring belt 14 and an underside of the combustion bowl 12.

A cover 16 is disposed along the bottom of cooling gallery 15. Cover 16 can be completely closed, as shown in FIG. 2, or can have an inlet aperture 17. Cooling oil 2, which also serves as the lubricating oil for the engine, is sprayed from a cooling nozzle (not shown), which is separately provided adjacent to the bottom of the piston 10. As shown in FIG. 3, the stream of cooling oil 2 from the nozzle is directed at the inlet aperture 17, in the bottom of the cooling gallery. The oil has been circulated through the engine and is cooler than the metal piston; therefore, the oil removes some of the heat from the piston. The oil then flows around the cooling gallery 15, and then drains back into the engine via the aperture 17, located on the bottom of the gallery on the opposite side from the oil inlet aperture

The resulting hot cooling liquid, which has reached the cooling oil aperture 17, flows out of the cooling gallery 15 in a downward direction, as illustrated in FIG. 3, and passes through the piston interior space. Then the oil is cooled and conditioned by a separately provided apparatus (not shown) before it is returned to the cooling liquid nozzle.

As shown in FIGS. 1-4, cooling fins 18 are present on the inner surface of combustion bowl 12. Cooling fins 18 extend circumferentially around an upper part of the interior wall of combustion bowl 12. In addition, as shown in FIGS. 1-3, cooling fins 19 can also be placed on the surface of cooling gallery 16, for additional cooling effect. As shown in FIG. 4, cooling fins 20 can also be placed on the underside of combustion bowl 12. Ribs 18 serve to diffuse the heat from the combustion bowl radially outward to the cooling gallery, so that the piston is cooled more efficiently. The addition of ribs 19, 20 increases this cooling effect.

In one embodiment of this invention, the cooling fins 18, 19, 20 that increase the surface area of the of the cooling gallery or combustion bowl, are machined into the surface. In another embodiment, cooling fins 18, 19, 20 are forged into the surface. In a further embodiment, cooling fins 18, 19, 20 are mounted or affixed to the surface via a mechanical method, such as by screws.

The present invention provides a simple, efficient way to diffuse the heat created by the high loads and stresses on the piston, which results in a piston that is less vulnerable to damage.

Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention. 

What is claimed is:
 1. A piston for an internal combustion engine, comprising: a piston head having a combustion bowl, a circumferential ring belt and a circumferential cooling gallery disposed between the combustion bowl and the ring belt; and pin bosses disposed below the piston head, said pin bosses each having a pin bore; wherein the combustion bowl has an interior surface with at least one fin disposed thereon.
 2. The piston according to claim 1, wherein the at least one fin extends circumferentially around an upper region of the combustion bowl.
 3. The piston according to claim 2, wherein said at least one fin comprises multiple fins.
 4. The piston according to claim 1, further comprising at least one fin disposed on an interior surface of the cooling gallery.
 5. The piston according to claim 1, further comprising at least one fin disposed underneath the combustion bowl.
 6. The piston according to claim 1, wherein the cooling gallery is open at a bottom and further comprising a cover for sealing the bottom.
 7. The piston according to claim 6, wherein the cover has an aperture for oil inlet and drainage.
 8. The piston according to claim 1, wherein the at least one fin is forged onto the surface of the combustion bowl.
 9. The piston according to claim 1, wherein the at least one fin is machined onto the surface of the combustion bowl.
 10. The piston according to claim 1, wherein the at least one fin is mounted or affixed to the surface via a mechanical method. 